AdAge has agency report cards. Goodby took top honors for agencies this year.
Communication Arts and the One Show display the best creative.
The Four As has annual agency rankings and awards as well.
AdWeek has frequent agency stats and an annual rundown.
AIGA has reports on design firms.
You want the best as in most creative or the best as in the most profitable? They're not always the same. Actually, they're seldom the same.